Transcriptomic and Metabolomic Analyses Provide Insights Into an Aberrant Tissue of Tea Plant (Camellia sinensis)

Tea plant (Camellia sinensis (L.) O. Kuntze) is one of the most important economic crops with multiple mutants. Recently, we found a special tea germplasm that has an aberrant tissue on its branches. To figure out whether this aberrant tissue is associated with floral bud (FB) or dormant bud (DB), we performed tissue section, transcriptome sequencing, and metabolomic analysis of these tissues. Longitudinal sections indicated the aberrant tissue internal structure was more like a special bud (SB), but was similar to that of DB. Transcriptome data analysis showed that the number of heterozygous and homozygous SNPs was significantly different in the aberrant tissue compared with FB and DB. Further, by aligning the unmapped sequences of the aberrant tissue to the Non-Redundant Protein Sequences (NR) database, we observed that 36.13% of unmapped sequences were insect sequences, which suggested that the aberrant tissue might be a variation of dormant bud tissue influenced by the interaction of tea plants and insects or pathogens. Metabolomic analysis showed that the differentially expressed metabolites (DEMs) between the aberrant tissue and DB were significantly enriched in the metabolic pathways of biosynthesis of plant hormones and biosynthesis of phenylpropanoids. Subsequently, we analyzed the differentially expressed genes (DEGs) in the above mentioned two tissues, and the results indicated that photosynthetic capacity in the aberrant tissue was reduced, whereas the ethylene, salicylic acid and jasmonic acid signaling pathways were activated. We speculated that exogenous infection induced programmed cell death (PCD) and increased the lignin content in dormant buds of tea plants, leading to the formation of this aberrant tissue. This study advanced our understanding of the interaction between plants and insects or pathogens, providing important clues about biotic stress factors and key genes that lead to mutations and formation of the aberrant tissue.

Sugar units, not chilling units, control endodormancy duration in plants; potato tuber as a case study

Endodormancy (ED) is a crucial stage in the life cycle of many perennial plants, regulated by genetic and environmental factors. Chilling units, growth regulators, and nutrient supply are considered inducers of ED release, but the mechanism governing ED duration is poorly understood. The potato tuber has been used as a model system to study metabolic processes associated with ED release. Cold-induced sweetening is a well-known response of the tuber to chilling. Here, we found that cold stress induces an increase in sugar units in association with plasmodesmatal closure in the dormant bud cells. Tuber sweetening was associated with shortened ED duration after cooling. Heat exposure also caused sugar unit accumulation followed by faster ED release. A logistic function was developed to predict ED duration based on sugar unit measurements. We discovered that ED release is better correlated with the accumulation of sugar units compared to chilling units. CRISPR/Cas9 knockout of the vacuolar invertase gene (StVInv) induced longer ED, but only in cultivars in which the mutation modified the level of sugar units. Our results suggest that sugar units are better predictors of vegetative bud ED duration than chilling units.

Cytokinin-promoted secondary growth and nutrient storage in the perennial stem zone of Arabis alpina

Perennial plants maintain their life span through several growth seasons. Arabis alpina serves as model Brassicaceae species to study perennial traits. A. alpina lateral stems have a proximal vegetative zone with a dormant bud zone, and a distal senescing seed-producing inflorescence zone. We addressed the questions of how this zonation is distinguished at the anatomical level, whether it is related to nutrient storage, and which signals affect the zonation. We found that the vegetative zone exhibits secondary growth, which we termed the perennial growth zone (PZ). High-molecular weight carbon compounds accumulate there in cambium and cambium derivatives. Neither vernalization nor flowering were requirements for secondary growth and sequestration of storage compounds. The inflorescence zone with only primary growth, termed annual growth zone (AZ), or roots exhibited different storage characteristics. Following cytokinin application, cambium activity was enhanced and secondary phloem parenchyma was formed in the PZ and also in the AZ. In transcriptome analysis cytokinin-related genes represented enriched gene ontology terms and were expressed at higher level in PZ than AZ. Thus, A. alpina uses primarily the vegetative PZ for nutrient storage, coupled to cytokinin-promoted secondary growth. This finding lays a foundation for future studies addressing signals for perennial growth.HighlightArabis alpina stems have a perennial zone with secondary growth, where cambium and derivatives store high-molecular weight compounds independent of vernalization. Cytokinins are signals for the perennial secondary growth zone.

To the issue of ash-leaved maple (Acer negundo L.) efficient use in the Moscow municipal forestry

The North American ash-leaved maple is one of the most dangerous invasive species in Russia. However, due to the high seed production and the ability to grow in the environmentally unfriendly territories, it spread widely in Moscow, forming the tangle of tilted and curved trees, which are not much decorative. The rapid reduction of the ash-leaved maple population may exacerbate the adverse environmental situation in the city. The study of the species’ biomorphological features, as well as the consequences of the spontaneous pruning performed by the landscapers, makes it possible to issue recommendations on adjusting the crowns of curved and tilted trees, multi-stem trees, as well as on improving the appearance of tangles. Thanks to the dormant buds, Acer negundo easily tolerates the most radical variants of rejuvenating pruning, allowing to reduce the crown of trees to a height of 3–4 m, to form low-growing trees with a height of 1.5–2 m, as well as living thickets, to correct the crown of tilted and bent trees by shortening the trunk to a powerful shoot arising on the trunk from a dormant bud, and removing, in case of a bifurcation of the trunk, the most deflected trunk.

Analysis of freezable water content by DSC for apple dormant bud cryopreservation

Dormant bud cryopreservation is a valuable tool for the germplasm of temperate trees preservation. Freezable water content, as an important cryopreservation characteristic, was analysed by DSC. Scions of modern apple tree varieties (Malus domestica) were collected during the winter season from orchards, freeze-dehydrated to 26–32% of water content at –5°C and cryopreserved by the two-step procedure. Samples were rehydrated in moist peat after 4 months of cryopreservation and grafted on rootstocks in a field. Regeneration by sprouting buds on rootstocks was evaluated. The varieties were divided into three groups according to their water content and percentage of crystallized water. The regeneration in the three groups decreased with decreasing bud water content. Regeneration was higher than 80% in most of the varieties and reached 100% in almost 1/3 of the tested varieties. In only one variety, was regeneration lower than 40%, which is still a high regeneration rate for considering apple genotypes as successfully cryopreserved. According to this study, the two-step cryoprotocol was successfully optimized for Central European conditions.

Auxin and cytokinin coordinate the dormancy and outgrowth of axillary bud in strawberry runner

Background Axillary buds allow the production of either vegetative or reproductive shoots, which display a plastic developmental potential of the plant to suit the prevailing environmental changes. Strawberry represents one of many plant species which displays horizontal above-ground growth of shoot development for asexual reproduction. Two distinct runner growth patterns exist in different strawberry species: one is called sympodial type such as Fragaria vesca, and the other one is called monopodial type such as Fragaria pentaphylla. Despite the runner growth morphology of these strawberry species have been well known, the mechanisms that determine the distinct patterns have rarely been reported. Results In this study, we used Fragaria vesca Hawaii-4 and Fragaria pentaphylla as model species, and captured the initiated dormant bud and non-dormant bud as materials to compare their transcriptome profiles and phytohormone content. Comparisons revealed that relatively higher auxin activity is present in the dormant bud and relatively higher cytokinin activity is in the non-dormant bud. Decapitation and pharmacological experiments on dormant buds showed that the reduction of auxin accumulation triggers the regeneration of vegetative shoots in dormant buds, and exogenous cytokinin application triggers cell fate turnover and generation of reproductive shoots. Conclusion Here, we uncover a mechanism by which auxin and cytokinin coordinate the dormancy and outgrowth of axillary bud in strawberry runner. Our results suggest a contrasting behavior of auxin and cytokinin in control of axillary bud development, facilitating a preliminary understanding of shoot architecture formation in strawberry.

In Vitro Propagation and Acclimatization of Dragon Tree (Dracaena draco)

In this study, an efficient in vitro procedure was developed for bud induction, rooting of developing shoots and greenhouse acclimatization of young plantlets of dragon tree (Dracaena draco). Effects of media (S1 (1 mg/L KIN and 1 mg/L NAA), S2 (3 mg/L KIN and 1 mg/L IAA), S3 (1 mg/L BAP and 2 mg/L IBA) and S4 (1 mg/L BAP and 1 mg/L NAA)) on shoot induction and media (R1 (0 mg/L IBA), R2 (0.5 mg/L IBA), R3 (1 mg/L IBA), and R4 (2 mg/L IBA)) on root induction were examined in order to find optimal plant hormone concentrations for efficient Dracaena draco dormant bud development and subsequent rooting. The best shoot induction and rooting media were S1 and S2, and R3 and R4, respectively. Dormant buds from one-year-old Dracaena draco plants submitted to this in vitro procedure allowed successful recovery of up to 8 individuals per explant used. In vitro grown plants were successfully acclimated in the greenhouse. The potential of this in vitro procedure for multiplication of this endangered tree is discussed in this report.

PhePEBP family genes regulated by plant hormones and drought are associated with the activation of lateral buds and seedling growth in Phyllostachys edulis

Development of lateral buds on the underground rhizome in moso bamboo is essentially the early stage of the development of aboveground branching, which is regulated by Phosphatidyl-Ethanolamine Binding Protein (PEBP) family genes, but it is unknown whether the PEBP family genes are involved in the activation and development of lateral buds underground. By scanning the whole-genome sequence of moso bamboo, we identified 25 PhePEBP family genes and amplified their full-length open reading frames (ORFs). A sequence analysis revealed that they are composed of four exons and three introns, except for PheFT10, which contains six exons and five introns. PheFT10 underwent alternative splicing, resulting in at least four transcripts (PheFT10α, PheFT10β, PheFT10γ and PheFT10δ). Although PhePEBP genes are generally expressed at low levels and show dramatically organ-specific expressions, the transcription levels of most PhePEBP genes, including the transcripts of PheFT10, change with plant age. Together with the observation that the expression of PhePEBP family genes can be regulated by plant hormones and drought, our data suggest that PhePEBP family genes might be involved in the activation of lateral buds and seedling growth. Particularly, PheFT9, PheTFL2 and PheTFL8 may play vital roles during the activation of dormant buds based on the analysis of amino acid substitution and expression profile. These findings provide insights for in-depth exploration of the biological functions of the PhePEBP family genes in regulating the activation of dormant bud and the development of seedling in moso bamboo.